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Iranians want a nuclear agreement

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Negotiators for Iran and six world powers resume nuclear talks in Vienna, Austria

They want to reach a permanent agreement on the future of Iran's nuclear program

An interim deal is due to expire in less than three weeks

U.S. secretary of state urges Iran's leaders to back up words with concrete actions

World powers and Iran resumed talks Thursday in Vienna, Austria, aimed at reaching a permanent deal on the future of Tehran's nuclear program ahead of a looming deadline.

This is the final round of talks before an interim six-month agreement reached between Iran and the so-called P5+1 group of nations -- the United States, the United Kingdom, France, China, Russia and Germany -- comes to an end July 20.

Iran's Foreign Minister Javad Zarif met with U.S. Deputy Secretary of State William Burns and EU foreign policy chief Catherine Ashton on Wednesday, ahead of the first full session Thursday.

Michael Mann, a spokesman for Ashton, told reporters in Vienna that the six world powers were committed to reaching an agreement ahead of the deadline.

He described the atmosphere at the talks as "very workmanlike, very serious, very determined" and said the negotiations would continue for "as long as it takes" for a deal to be forged. The deadline could potentially be extended.

Ashton also met Thursday with the head of the U.N. nuclear watchdog, the International Atomic Energy Agency, which would play a key role in the implementation of a final agreement, Mann said.

Under the interim deal, Iran cut back on parts of its nuclear program and the six nations reduced economic sanctions.

"All along, these negotiations have been about a choice for Iran's leaders," he wrote.

"They can agree to the steps necessary to assure the world that their country's nuclear program will be exclusively peaceful and not be used to build a weapon, or they can squander a historic opportunity to end Iran's economic and diplomatic isolation and improve the lives of their people.

"Diplomacy and leadership are marked by tough calls. This shouldn't be one of them."

However, despite all the months of talks, Western negotiators still don't know which way Iran will go, Kerry said -- and a discrepancy remains between what the Iranians say they want from their nuclear program and the content of that program so far.